Glued laminated timber is often called Glulam and is manufactured as timber laminations
bonded together using adhesive. Glulam can be made to almost
any size and used for a wide variety of structural features including arches, portals, roof, lintel and floor beams,
for columns, rafters and 'A' frames etc etc Glulam structural members can
make use of smaller and less desirable dimensions of timber, yet are engineered to be stronger than similarly
sized members made of solid wood. They also suffer less than solid timbers from defects and movement
due to moisture changes such as checking, warping and twisting. The laminations used
are also generally of a more uniform quality compared to solid timber sections.

Compared to most structural materials, Glulam
has a relatively high strength per unit weight. It can be used to produce a lighter superstructure, compared to steel or concrete, with a consequent economy in foundation construction.
Glulam will not corrode. It also has a high
resistance to chemical attack and aggressive and polluted environments.

Glulam is manufactured in accordance with BS En 14080. The timber used is graded in accordance with BS EN 14081.
The various parameters required to design using this material are covered in BS 5268-2 2002 section 3

This type of laminate is designed to resist loads normal to the plane of the laminates. The grades stress for horizontally glued timber laminations is obtained as the product of the
relevent stresses found in tables and the relevant modification factors found in the table. Modification factors for horizontally glued single grade laminates

It should be noted that the modification factors K7, and K14 apply to the size of the glulam section and not to the timber
lamination size.

Horizontal Timber Glued Laminate - all one grade

The above rule cover only applies when laminations of one strength grade only used.
It is acceptable to use laminations of different grades when the grades are up to two grades apart and when a
maximum of 25% of the depth at the top and bottom of the section are of the superior grade. When
timbers of different grades are use the calculated grades stresses relevant to bending tension and compression,
parallel to the grain, should be multiplied by 0,95. The calculated grade stress for shear
parallel to the grain should be multiplied by 0,8

Horizontal Timber Glued Laminate - combined grades

Summerising the derivation of the relevant permissible stresses for the glued laminate sections..

Modulus of Elasticity
For single and combined grade glulam ..EGlulam = Emean. K20

Vertically glued laminates

This type of laminate is designed to resist loads parallel to the plane of the laminates. The grades stress for horizontally glued timber laminations is obtained as the product of the
relevent stresses found in tables and the relevant modification factors found in the table. Modification factors for vertically glued single grade laminates

It should be noted that the modification factors K7, and K14 apply to the size of the glulam section and not to the timber
lamination size.

Summerising the derivation of the relevant permissible stresses for the glued laminate sections..

Bending parallel to grainσm.adm,ll = σm,g,ll. K2.K3.K6.K7.K8.K27

Tension parallel to grainσt.adm,ll = σt,g,ll. K2.K3.K8.K14.K27

Shear parallel to grainτt.adm,ll = τt,g,ll. K2.K3.K5K8.K27

Compression parallel to grainσc.adm,ll = σc,g,ll. K2.K3.K8.K12.K28

Compression normal to grainσc.adm,l- = σc,g,l-. K2.K3.K4.K8.K29

Modulus of Elasticity
.EGlulam = Emean

Glued end joints relevant to glued laminated timber

According to BS 5268-2, finger joints, used to produce longer gluded laminated beam lengths from shorter lengths, should have characteristic bending strengths of not less than the characteristic bending
strength of the strength class for the lamination when tested in accordance with
BS EN 385.

Note : As identified on webpage Timber design the characteristic bending strength is the ultimate strength of the timber prior to
inclusion of the various safety margins and is identified as the number in the grading system e.g a c14 strength graded timber has a characteristic bending strenth
of 14 N/mm2